The present invention relates to an improved fastening lug and, more particularly, to a vibration tolerant, torque-limiting lug exhibiting increased thread strength.
Fastening lugs are used in several applications. One well known application is the use of a lug to both mechanically fix and electrically couple a grounding wire to a metal structure. The lugs used for such an application are often referred to as "grounding lugs." One commonly encountered commercial application involves the installation of a grounding conductor (pursuant to electrical code) between fittings used to terminate and/or couple non-metallic conduit. In the aforementioned application, the grounding lug itself is mechanically coupled to a portion of the fitting, e.g., the gland nut of the fitting.
With respect to fastening lugs and, more particularly grounding lugs, it will be recognized by those skilled in the art that it is a common design goal to reduce the amount of material used to form the lug. Inasmuch as the cost of material represents a substantial portion of the total cost of the lug, a reduction in the amount of material used to form the component can produce significant cost savings. However, it will be also recognized that a reduction in the wall thickness of the stock material used to form the lug will significantly decrease the strength of the structure, thus rendering such structure prone to failure from deformation of the lug and/or to thread failure from overtightening of the set-screw.
An additional problem encountered with fastening lugs and, particularly grounding lugs, concerns the tendency of the fastener (e.g., the set-screw) to "back-out" of the threaded opening formed in the housing of the lug during shipping/handling of the lug. Specifically, vibration encountered during shipping/handling of the fastening lugs is often sufficient to produce the aforementioned back-out, causing the set-screw to disassemble from the housing of the lug. This disassembly is both bothersome and time consuming to the installer. Prior art techniques such as "staking" of the set screw address the problem of back-out, but are relatively costly. Other techniques such as tightening the set-screw prior to shipping require the installer to first perform the time consuming step of untightening the set-screw before insertion of the grounding conductor.
There is therefore a need in the art for a fastening lug which allows the fabrication of such lug from thinner walled stock material, but which provides a structure which resists deformation failure due to overtightening of the set-screw. There is a further need in the art for a fastening lug which includes a threaded passage of increased length and increased thread strength, and which allows use of larger diameter set screw. Finally, there is a need in the art for a fastening lug which allows shipping and handling of the lug without back-out of the set-screw and without staking and/or requiring complete tightening of the set-screw.